Forming Polyesters
- Addition polymerisation has been covered in reactions of alkenes
- They are made using monomers that have C=C double bonds joined together to form polymers such as polyethene
- Condensation polymerisation is another type of reaction whereby a polymer is produced by repeated condensation reactions between monomers
- Natural condensation polymers are all formed by elimination of water
- Although the process of condensation polymerisation involves the elimination of a small molecule
- Condensation polymers can be identified because the monomers are linked by ester or amide bonds
Polyester
- Is formed by the reaction between dicarboxylic acid monomers and diol monomers
- Polyester is produced by linking these monomers with ester bonds / links
This polymer structure shows an ester functional group linking monomers together
Formation of polyesters
- A diol and a dicarboxylic acid are required to form a polyester
- A diol contains 2 -OH groups
- A dicarboxylic acid contains 2 -COOH groups
The position of the functional groups on both of these molecules allows condensation polymerisation to take place effectively
- When the polyester is formed, one of the -OH groups on the diol and the hydrogen atom of the -COOH are expelled as a water molecule (H2O)
- The resulting polymer is a polyester
- In this example, the polyester is poly(ethylene terephthalate) or PET, which is sometimes known by its brand names of Terylene or Dacron
Expulsion of a water molecule in this condensation polymerisation forms the polyester called (ethylene terephthalate) (PET)
Formation of polyesters - hydroxycarboxylic acids
- So far the examples of making polyesters have focused on using 2 separate monomers for the polymerisation
- There is another route to making polyesters
- A single monomer containing both of the key functional groups can also be used
- These monomers are called hydroxycarboxylic acids
- They contain an alcohol group (-OH) at one end of the molecule while the other end is capped by a carboxylic acid group (-COOH)
Both functional groups that are needed to make the polyester come from the same monomer
